Optically controlled MEMS switch and method of using the same

ABSTRACT

The present embodiments are directed towards the optical control of switching an electrical assembly. For example, in an embodiment, an electrical package is provided. The electrical package generally includes a micro electromechanical systems (MEMS) device configured to interface with an electrical assembly, the MEMS device being operable to vary the electrical assembly between a first electrical state and a second electrical state, a MEMS device driver in communication with the MEMS device and being operable to produce high voltage switching logic from an electrical signal, and an optical detector in communication with the MEMS device driver and configured to produce the electrical signal from an optical signal produced by a light source in response to an applied current-based electrical control signal.

BACKGROUND

The subject matter disclosed herein relates to switching devices usingoptical input, and more specifically to hardening the mechanical motionof a micro electromechanical systems (MEMS) device from electromagneticinterference.

Electronic switches are typically employed for the purpose of varying anelectrical circuit between conducting states. Some switches, especiallythose with high impedance drive circuits, can be inadvertently activatedwith electro magnetic (EM) interference. For example, EM interferencecan couple onto switch drive logic connections, which are typically highinput impedance circuits, and cause spurious switching logic transients.The switching logic transients, in turn, cause unintended switchactivation. Some approaches to avoid the production of spuriousswitching logic transients include filtering the switch drive logiclines to mitigate EM interference coupling using L-C or R-C networks.However, some switches, such as micro electromechanical system(MEMS)-based switches, may operate at high frequencies such thatconventional filtering technologies may not be able to operate atsufficient rates to be useful in MEMS applications. One example of sucha system in which a switch may experience EM interference is a magneticresonance imaging (MRI) system.

In MRI systems, a highly uniform, static magnetic field is produced by aprimary magnet to align the spins of gyromagnetic nuclei within asubject of interest (e.g., hydrogen in water/fats). The nuclear spinsare perturbed by a radiofrequency (RF) transmit pulse, encoded based ontheir position using gradient coils, and allowed to equilibrate. Duringequilibration, faint RF fields are emitted by the spinning, processingnuclei and are detected by a series of RF coils. The signals resultingfrom the detection of the RF fields are then processed to reconstruct auseful image.

The MRI system may include features to prevent damage to certain of theRF coils, such as those that receive faint RF signals from within apatient, while the RF transmit pulse and/or gradient pulses are beingperformed. Typically, blocking signals are provided to the receivingcoils to prevent resonance with the RF transmit and gradient pulses,which can result in eddy currents, heat production, image artifacts, andpotential damage to various electrical components. However, as notedabove, some high impedance drive circuits employed in conjunction withswitches that allow the blocking signals to be provided to the coils canexperience spurious switching logic transients. The transients mayresult in the receiving coil being converted to a resonant state, whichcan be undesirable during certain phases of operation of the MRI system.Accordingly, a need exists for improved EM-hardened techniques forswitching electrical circuits, such as those present in MRI systems.

BRIEF DESCRIPTION

In one embodiment, a magnetic resonance imaging (MRI) system isprovided. The system generally includes a transmitting coil configuredto transmit RF energy into a subject of interest, a receiving coilcapable of being switched between at least a first state, in which thereceiving coil can resonate in response to RF signals generated withinthe subject of interest, and a second state, in which the receiving coilis unable to resonate in response to RF energy produced by thetransmitting coil, a switch configured to vary the receiving coilbetween the first and second states in response to a logic signal, adevice driver configured to produce the logic signal in response to anelectrical signal, and an opto-isolator configured to produce theelectrical signal in response to a current-based control signal.

In another embodiment, a single electrical package is provided. Theelectrical package generally includes a micro electromechanical systems(MEMS) device configured to interface with an electrical assembly, theMEMS device being operable to vary the electrical assembly between afirst electrical state and a second electrical state, a MEMS devicedriver in communication with the MEMS device and being operable toproduce high voltage switching logic from an electrical signal, and anoptical detector in communication with the MEMS device driver andconfigured to produce the electrical signal from an optical signalproduced by a light source in response to an applied current-basedelectrical control signal.

In a further embodiment, a method for switching an electrical assemblyis provided. The method includes converting a current-based controlsignal into an optical signal using a light source, converting theoptical signal into an electrical signal using a light detector,converting the electrical signal generated by the light detector intoswitching logic, said switching logic generated by a device driver,converting the switching logic into mechanical motion to switch theelectrical assembly between a first conductive state and a secondconductive state using a micro electromechanical systems (MEMS) device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is an illustration of an embodiment of a MRI system utilizing oneor more receiving coils having an optically controlled MEMS device;

FIG. 2 is a block diagram illustration of a switching assembly in whicha surface mount package including a MEMS device, a device driver, and anopto-isolator is configured to receive current-based signals to switchan RF receiving coil between conductive states;

FIG. 3 is a diagrammatical illustration of the surface mount package ofFIG. 2;

FIG. 4 is a block diagram illustration of a switching assembly in whicha light source is in optical communication with a surface mount packagehaving a MEMS device, a device driver, and an optical detector, thelight source being disposed on a coil side of the assembly andconfigured to receive current-based signals to generate an opticalsignal to switch an RF receiving coil between conductive states;

FIG. 5 is a block diagram illustration of a switching assembly in whicha light source is in optical communication with a surface mount packagehaving a MEMS device, a device driver, and an optical detector, thelight source being disposed on a system side of the assembly andconfigured to receive current-based signals to generate an opticalsignal to switch an RF receiving coil between conductive states; and

FIG. 6 is a process-flow diagram of a method for switching an electricalassembly between conductive states using an optically controlled MEMSdevice.

DETAILED DESCRIPTION

The approaches embodied herein overcome the shortcomings mentionedabove, among others, by providing embodiments directed towards theoptical control of switching in electrical assemblies. For example, itmay be desirable to integrate a device capable of creating a physicaldisconnect into an electrical circuit, such as a resonant coil within anMRI system, so as to vary the electrical circuit between conductivestates (i.e., between resonant and non-resonant states). Due to theirhigh frequency of operation, MEMS devices can provide an attractiveapproach for creating such physical disconnects. For example, typicalMEMS devices operate at frequencies such as between about 1 and 10microseconds per switching event. Unfortunately, typical filteringapproaches aimed towards mitigating EM interference with logic-carryingelectrical features (i.e., logic connections) do not operate atsufficient speeds to allow their combination with MEMS devices. As anexample, the timeframe of such filtering approaches can range anywherefrom about 100 microseconds up to a millisecond, or more than an orderof magnitude higher than the operation of the MEMS device.

In accordance with presently contemplated embodiments, in lieu of, or inaddition to, performing such filtering operations, a MEMS device may beswitched using a current-signaling based opto-isolator capable ofelectrically isolating the MEMS device, and the driver that provides theswitching logic to the MEMS device, from control circuitry that controlsthe operation of the MEMS device. Indeed, as used herein, the term“opto-isolator” refers to a feature capable of transferring electricalsignals via one or more optical signals. Thus, the opto-isolatorprovides coupling of an electrical source and an electrical output, suchas a control signal source and a switch, while providing electricalisolation therebetween. In this way, the opto-isolator may also bereferred to as an optocoupler, a photocoupler, or an optical isolator.In the present context, such isolation may provide enhanced preventionof electromagnetic interference (EMI).

It should be noted that by providing current-based control signals asopposed to voltage-based control signals, a light source within theopto-isolator will not be activated in response to EM energy producedduring transmit sequences performed by the MRI system. In this way,spurious switching of the MEMS device, and thus the electrical assembly,can be avoided. More specifically, in an embodiment, a control circuitmay provide a current control signal to operate an opto-isolator. Theopto-isolator, during operation, produces an EM-immune beam of lightthat is converted into an electrical signal. A MEMS switch driver maythen convert this electrical signal into switching logic for the MEMSdevice. As noted above, this allows the control circuit to beelectrically isolated from the MEMS switch driver and MEMS device. Itshould be appreciated that while the present disclosure is applicable toany number of electrical assemblies, such as field effect transistors(FETs) or other electrical arrays, and is not limited to any particularimplementation, various aspects of the present approaches are presentedin the context of magnetic resonance imaging (MRI) systems so as toprovide meaningful examples of one possible implementation.Specifically, the embodiments described herein are directed towards anoptically controlled and current-driven switch configured to vary aresonant loop between resonant states.

Accordingly, the implementations described herein may be performed by amagnetic resonance imaging (MRI) system, wherein specific imagingroutines are initiated by a user (e.g., a radiologist). Further, the MRIsystem may perform data acquisition, data construction, and imagesynthesis. Accordingly, referring to FIG. 1, a magnetic resonanceimaging system 10 is illustrated schematically as including a scanner12, a scanner control circuit 14, and a system control circuitry 16.System 10 additionally includes remote access and storage systems ordevices as picture archiving and communication systems (PACS) 18, orother devices such as teleradiology equipment so that data acquired bythe system 10 may be accessed on- or off-site. While the MRI system 10may include any suitable scanner or detector, in the illustratedembodiment, the system 10 includes a full body scanner 12 having ahousing 20 through which a bore 22 is formed. A table 24 is moveableinto the bore 22 to permit a patient 26 to be positioned therein forimaging selected anatomy within the patient 26. The selected anatomy maybe imaged by a combination of patient positioning, selected excitationof certain gyromagnetic nuclei within the patient 26, and by usingcertain features for receiving data from the excited nuclei as they spinand precess, as described below.

Scanner 12 includes a series of associated coils for producingcontrolled magnetic fields for exciting the gyromagnetic material withinthe anatomy of the subject being imaged. Specifically, a primary magnetcoil 28 is provided for generating a primary magnetic field generallyaligned with the bore 22. When the patient 26 is placed within thescanner 12, the gyromagnetic nuclei equilibrate their magnetization bygenerally aligning their spins perpendicular to the field of the primarymagnet coil 28. A series of gradient coils 30, 32, and 34 permitcontrolled magnetic gradient fields to be generated for positionalencoding of certain of the gyromagnetic nuclei during examinationsequences. A radio frequency (RF) coil 36 is provided for generatingradio frequency pulses for exciting the certain gyromagnetic nucleiwithin the patient. In addition to the coils that may be localized toand/or within the scanner 12, the system 10 also includes a set ofreceiving coils 38 configured for placement proximal to the patient 26.As an example, the receiving coils 38 can includecervical/thoracic/lumbar (CTL) coils, head coils, and so forth.Generally, the receiving coils 38 are placed close to or on top of thepatient 26 so as to receive the weak RF signals (weak relative to thetransmitted pulses generated by the scanner coils) that are generated bycertain of the gyromagnetic nuclei within the patient 26 as they returnto alignment with the field generated by the primary coil magnet 28. Inaccordance with present embodiments, the receiving coils 38 may beswitched off so as not to receive or resonate with the transmit pulsesgenerated by the scanner coils, and may be switched on so as to receiveor resonate with the RF signals generated by the relaxing gyromagneticnuclei.

The various coils of system 10 are controlled by external circuitry togenerate the desired field and pulses, and to read emissions from thegyromagnetic material in a controlled manner. That is, in someembodiments, the circuitry may be disposed at a distance away fromscanner 12 so as to avoid any interference resulting from thetransmitted RF pulses and/or the bulk magnetic field. Such a distancemay include having the circuitry in a separate room, at a separatefacility, and so on. In the illustrated embodiment, a main power supply40 provides power to the primary field coil 28. A driver circuit 42 isprovided for pulsing the gradient field coils 30, 32, and 34. Such acircuit typically includes amplification and control circuitry forsupplying current to the coils as defined by digitized pulse sequencesoutput by the scanner control circuit 14. Another control circuit 44 isprovided for regulating operation of the RF coil 36. Circuit 44 includesa switching device for alternating between the active and inactive modesof operation, wherein the RF coil 36 transmits and does not transmitsignals, respectively. Circuit 44 also includes amplification circuitryfor generating the RF pulses. In accordance with the present approaches,the receiving coils 38 are connected to an optically controlled switch46 that is capable of switching the receiving coils 38 between receivingand non-receiving modes. That is, in some embodiments the opticallycontrolled switch 46 varies the receiving coils 38 between conductivestates, such that the receiving coils 38 resonate with the RF signalsproduced by relaxing gyromagnetic nuclei from within the patient 26while in the receiving state, and they do not resonate with RF energyfrom the transmitting coils (i.e., coil 36) so as to prevent undesirableoperation while in the non-receiving state. The optically controlledswitch 46 can include a light source, a light detector, and a switchoperatively connected to the light detector, for example via a driver.In one presently contemplated embodiment, the optically controlledswitch 46 may be a single surface mount (SMT) package that is configuredfor integration with the receiving coils 38 (i.e., via a retrofitoperation). Additionally, a receiving circuit 48 is provided forreceiving the data detected by the receiving coils 38, and may includeone or more multiplexing and/or amplification circuits. Theconfiguration of the optically controlled switch 46 and its interfacewith the receiving coils 38 is described in further detail below.

Scanner control circuit 14 includes an interface circuit 50 foroutputting signals for driving the gradient field coils 30, 32, 34 andthe RF coil 36. Additionally, interface circuit 50 receives the datarepresentative of the magnetic resonance signals produced in examinationsequences from the receiving circuitry 48 and/or the receiving coils 38.The interface circuit 50 is operatively connected to a control circuit52. The control circuit 52 executes the commands for driving the circuit42 and circuit 44 based on defined protocols selected via system controlcircuit 16. Control circuit 52 also serves to provide timing signals tothe optically driven switch 46 so as to synchronize the transmission andreception of RF energy. Further, control circuit 52 receives themagnetic resonance signals and may perform subsequent processing beforetransmitting the data to system control circuit 16. Scanner controlcircuit 14 also includes one or more memory circuits 54, which storeconfiguration parameters, pulse sequence descriptions, examinationresults, and so forth, during operation. Interface circuit 56 is coupledto the control circuit 52 for exchanging data between scanner controlcircuit 14 and system control circuit 16. Such data will typicallyinclude selection of specific examination sequences to be performed,configuration parameters of these sequences, and acquired data, whichmay be transmitted in raw or processed form from scanner control circuit14 for subsequent processing, storage, transmission and display.

An interface circuit 58 of the system control circuit 16 receives datafrom the scanner control circuit 14 and transmits data and commands backto the scanner control circuit 14. The interface circuit 58 is coupledto a control circuit 60, which may include one or more processingcircuits in a multi-purpose or application specific computer orworkstation. Control circuit 60 is coupled to a memory circuit 62, whichstores programming code for operation of the MRI system 10 and, in someconfigurations, the processed image data for later reconstruction,display and transmission. An additional interface circuit 64 may beprovided for exchanging image data, configuration parameters, and soforth with external system components such as remote access and storagedevices 18. Finally, the system control circuit 60 may include variousperipheral devices for facilitating operator interface and for producinghard copies of the reconstructed images. In the illustrated embodiment,these peripherals include a printer 66, a monitor 68, and user interface70 including devices such as a keyboard or a mouse.

While the present approaches will be described in the context of MRIsystem 10 so as to facilitate discussion, it should be noted that theMRI system 10 is merely intended to be one example, and other systemtypes, such as so-called “open” MRI systems, may also be used.Similarly, such systems may be rated by the strength of their primarymagnet, and any suitably rated system capable of carrying out the dataacquisition and/or processing described below may be employed. Indeed,the systems described below with respect to FIGS. 2-5 may be applicableto any electrical assembly, or, in the context of MRI, any coil arraycapable of being switched between resonant states.

Moving now to FIGS. 2-5, embodiments of switching assemblies areillustrated, the switching assemblies being generally configured toswitch a resonant loop between a state where the loop is able toresonate with RF energy and a state where the loop is unable to resonatewith RF energy. The switching assemblies may be included as a part of aMRI system, or may be provided as part of a kit so as to retrofit anexisting coil array for optical control of switching. Moreover, theswitching assembly embodiments, while described in the context ofreceiving coil arrays, are also applicable to any number of coils, suchas transmitting coil arrays and so forth.

FIG. 2 illustrates an embodiment of a switching assembly 80 havingfeatures for controlling the switching of a resonant loop 82. Generally,in accordance with presently contemplated embodiments, control signalsare generated at a system side 84, and the control signals are convertedinto light, transmitted via an optical medium, and re-converted into anelectrical signal for producing switching logic (which causes a MEMSswitch 88 to switch the resonant loop 82) at a coil side 88. Thedivision between the system side 84 and the coil side 88 is generallydepicted as a line 90. In the embodiment illustrated in FIG. 2, anelectrical package 92 (e.g., a surface mount (SMT) or a through holepackage) includes features for providing electrical isolation, EMimmunity, and switching logic signals. Specifically, the electricalpackage 92 illustrated in FIG. 2 may be a single package (i.e., a singleboard) including an opto-isolator 94, a MEMS switch driver 96 incommunication with the opto-isolator 94, and the MEMS switch 86 incommunication with the MEMS switch driver 96 that is configured tointerface with the resonant loop 82. It will be appreciated that the useof a SMT or through hole package may allow facile integration with MRIcoil architectures, pick-and-place assembly onto such architectures, andcan be readily manufactured based on existing metal oxidesemiconductor-field effect transistor (MOSFET) technologies. As anexample, the electrical package may have a ball grid array (BGA)configuration, a dual inline package (DIP) configuration, a gull wingconfiguration, a butterfly configuration, and so on that is capable ofinterfacing with an electrical assembly. One embodiment of such anelectrical package is described in further detail with respect to FIG. 3below.

As noted above, control signals are generated from the system side 84 ofthe assembly 80. These control signals are provided to the electricalpackage 92 as a control input for generating the switching logic for theMEMS switch 86. For example, during operation, the opto-isolator 94 mayreceive control signals generated from a multiplexer board 98. Themultiplexer board 98, in some embodiments, may also receive andmultiplex magnetic resonance data received at the loop 82. The controlsignals produced by the multiplexer board 98 are then routed through apreamplifier 100, and on to the opto-isolator 94. More specifically, thecontrol signals are sent via a current control signal (e.g., via lowimpedance differential current control signaling) to a light source 102of the opto-isolator 94. It should be noted that such current signalingmay provide enhanced EMI immunity over other signaling techniques, suchas voltage-driven signaling. For example, as noted above, EMI may coupleonto signaling lines, such as one or more electrical connections betweenthe amplifier 100 and the light source 102. When current-based signalingis not utilized, such as in voltage signaling applications, the EMI maycause the light source 102 to inadvertently activate, which can causespurious switching logic to be produced and sent to the MEMS switch 86.Thus, in accordance with the present disclosure, the light source 102 isless prone to inadvertent activation by using current signaling ratherthan voltage signaling. Indeed, in accordance with presentlycontemplated embodiments, the current control signals may bedifferential control signals operating at between about 5 milliamps (ma)and 20 ma at a voltage of between about 1 volts (V) and 3 V.

The light source 102 may be a light emitting diode (LED) such as a laserdiode or similar light emitting feature that is substantially immune toRF energy. The light source 102 is configured to receive the controlsignals from the system side 84, which may include various systemconnectors local to the MRI system 10 described above, as well asvarious processing and interface circuitry. The light source 102, inresponse to the received current control signals, produces an opticalsignal, which is generally depicted as arrows 104. The optical signal104 can include a single wavelength or multiple wavelengths, and isdirected through space across a small distance (e.g., a few microns(μm)) towards an optical transducer, such as a photodetector 106 withinthe opto-isolator 94. Advantageously, the optical signal 104 issubstantially immune to EMI, and in the present context, may includewavelengths in the infrared (IR), near-IR, visible, and/or ultraviolet(UV) portion of the electromagnetic spectrum.

As an example, the photodetector 106 can include a diode array,photomultiplier tube or similar feature configured to produce electricalsignals when photons strike the detector 106. The electrical signalsthat are generated at the photodetector 106 may include high impedance,low power signals that are sent to the MEMS switch driver 96. As anexample, the signals may be at a current between about 1 nanoamp (nA)and 5 nA, at a voltage of between about 50 V and 150 V. In someembodiments, which are discussed in further detail below, the proximityof the photodetector 106 to the MEMS switch driver 96 may also result ina reduced probability of EMI coupling with one or more lines 108connecting the photodetector 106 to the MEMS switch driver 96.

In the illustrated embodiment, the opto-isolator 94 and the MEMS switchdriver 96 are each placed onto a printed circuit board (PCB) as part ofthe electrical package 92. For example, the opto-isolator 94 may bedisposed at a distance of about 1 mm to about 20 mm away from the MEMSdevice driver 96. Such a distance may facilitate communication betweenthe opto-isolator 94 and the MEMS switch driver 96 and allow theelectrical package to be of a single piece construction. The MEMS switchdriver 96 is generally configured to receive the output from theopto-isolator 94, and condition the received electrical signals intologic appropriate for the MEMS switch 86. For example, the MEMS switchdrier 96 may enable high voltage switching logic to the MEMS switch 86,which causes it to switch. In accordance with some embodiments, the MEMSswitch 86 can include one or more MEMS assemblies each having respectiveprinted circuit boards, switches, interconnects, and so forth.Generally, the MEMS switch 86 is configured to produce mechanical motionas a result of receiving the switching logic from the MEMS switch driver96. In the present context, the MEMS switch 86 serves to vary the loop82 between a coupled and a decoupled state by transitioning between aclosed and an open state. As an example, the MEMS switch 86 maytransition from an open to a closed state upon receiving the inputsignals, which causes the loop 82 to switch from a decoupled(non-resonant) state to a coupled (resonant) state. The MEMS switch 86may interface with the loop 82 using features known in the art, such asvia contact pads or similar interfacing standard.

As noted above, FIG. 3 illustrates an embodiment of the electricalpackage 92 (e.g., a SMT package) wherein the opto-isolator 94, the MEMSswitch driver 96, and the MEMS switch 86 are all integrated into asingle unit. In the illustrated embodiment, the opto-isolator 94includes a light emitting diode 120 that produces an optical signal inresponse to a current induced by a biasing voltage. The optical signalis detected by a diode 122, which produces electrical signals thattrigger high voltage MOSFET totem pole drivers 124 within the MEMSswitch driver 96. This triggering enables high voltage switching logicto be provided to the MEMS switch 86, causing an electrical junction 126of the MEMS device to open or close.

FIG. 4 illustrates an embodiment of a system 140 similar to thatillustrated in FIG. 2, but having the light source 102 coupled to thelight detector 106 by way of one or more waveguides 142, such as by oneor more optical fibers. Keeping in mind the operation of the system 80,the system 140 includes similar features for switching the resonant loop82 between resonant states. In accordance with the embodimentillustrated in FIG. 4, such features include the MEMS switch 86, MEMSswitch driver 96, and the photodetector 106, all of which are integratedonto a single SMT package 144. It should be noted that while the lightsource 102 is not part of the SMT package 144, it is disposed on thecoil side 88 of the system 140, for example at another area on theresonant loop 82.

In a similar manner to the configuration described with respect to FIG.2, the light source 102 receives current control signals (e.g.,differential current control signals) from one or more features as apart of or local to the system side 84. In system 140, the multiplexer98 and amplifier 100 provide the current control signals generated bycontrol circuitry to the light source 102. As above, the multiplexerboard 98 may generate or otherwise relay one or more control signals tothe light source 102 via preamplifier 100. The light source 102 producesa light beam that is transmitted down the optical waveguide 142 and tothe photodetector 106. It should be noted that the length of the opticalwaveguide 142 may be at least partially determined by the length betweenthe light source 102 and the photodetector 106. Keeping in mind that inthe illustrated embodiment of FIG. 4 the light source 102 is local tothe coil side 88, the optical waveguide 142 may be millimeters,centimeters, decimeters, or meters long. Moreover, in some embodiments,the optical waveguide 142 may interface or otherwise connect to the SMTpackage 144 using optical communication and/or connection features knownin the art. Alternatively, in an embodiment, the optical waveguide 142may terminate proximal to the photodetector 106.

In embodiments where the photodetector 106 and the light source 102 areseparate (i.e., are not part of a single opto-isolator component), itmay be desirable to integrate the photodetector 106 to be part of theMEMS switch driver 96. For example, as noted above with respect to FIG.2, in accordance with some presently contemplated embodiments, thephotodetector 106 and the MEMS switch driver 96 may be disposed at adistance from one another that is suitable for preventing EMI couplingto the one or more lines 108 connecting the photodetector 106 to theMEMS switch driver 96. For example, the photodetector 106 may be at adistance from the MEMS switch driver 96 of between about 1 μm and 20 μm,which reduces the probability of the lines 108 coupling with EMI. Insuch an embodiment, the MEMS switch driver 96 and the photodetector 106may be part of a monolithic optical gate turn on (optical GTO) devicedriver.

FIG. 5 depicts an embodiment of a system 150 having the light source 102disposed at the system side 84, rather than the coil side 88. Forexample, the light source 102 may be disposed local to the MRI system10, or may be positioned in an adjacent room or in another room in thefacility housing the MRI system 10. It will be appreciated that bypositioning the light source 102 a distance away from the MRI scanner 12that is greater than the separation depicted in the embodiments of FIGS.2-4, larger levels of EMI immunity may be realized. Indeed, in systemswhere the light source 102 is disposed across a room, in another room,or at another facility, the probability of EMI coupling to the logicconnections decreases drastically. Of course, such a configuration mayrequire longer lengths of optical waveguides (e.g., longer opticalfibers) than would be required if the light source 102 were disposedproximate or on top of the resonant loop 82. In FIG. 5, the beam oflight produced by the light source 102 is transmitted down an opticalwaveguide 152 having a length from about 0.5 meters up to a kilometer ormore. It should therefore be noted that the present embodiments providethe capability for the light source 102 to produce the beam of light ata facility that is separate from the MRI scanner 12 (FIG. 1) by a remoteoperator.

As noted above, the embodiments described herein may be applicable to anumber of electrical circuits and/or electrical assemblies. Accordingly,moving now to the process flow diagram illustrated in FIG. 6, thepresent disclosure also provides an embodiment of a method 160 foroptically controlling the switching of an electrical assembly. Themethod 160 includes sending one or more current-based control signals(e.g., differential current control signals) to a light source, such asan LED or similar feature (block 162). In response to the current, thelight source produces a light beam (block 164). The light beam can betransmitted down one or more optical waveguides (e.g., one or moreoptical fibers), or through any substantially transparent medium such asair, and to an optical transducer, such as a photodetector.

The photodetector detects the light beam (block 166), and produces anelectrical signal in response to the detected light beam (block 168).The electrical signal is then sent to a driver, such as a high voltageswitch driver (e.g., a high voltage MEMS driver). The high voltagedriver then converts the electrical signals into high voltage switchinglogic (block 170). The logic signal is provided to a MEMS switch or anarray of MEMS switches. As a result of receiving the logic signals, theMEMS switches produce mechanical motion to vary conductive states of theelectrical assembly to which they are connected (block 172). As anexample, the MEMS switches may move from an open to a closed state uponreceiving the input signals, which results in the completion of anelectrical circuit, such as a resonant loop. When the resonant loop iscompleted, it may be in a resonant state, as opposed to a non-resonantstate when the MEMS switch or switch array is open.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. It should also beunderstood that the various examples disclosed herein may have featuresthat can be combined with those of other examples or embodimentsdisclosed herein. That is, the present examples are presented in such asway as to simplify explanation but may also be combined one withanother. The patentable scope of the invention is defined by the claims,and may include other examples that occur to those skilled in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

The invention claimed is:
 1. A magnetic resonance imaging (MRI) system,comprising: a transmitting coil configured to transmit RF energy into asubject of interest; a receiving coil capable of being switched betweenat least a first state, in which the receiving coil can resonate inresponse to RF signals generated within the subject of interest, and asecond state, in which the receiving coil is unable to resonate inresponse to RF energy produced by the transmitting coil; a switchconfigured to vary the receiving coil between the first and secondstates in response to a logic signal, wherein the switch comprises amicro electromechanical systems (MEMS) switch; a MEMS device driverconfigured to produce the logic signal in response to an electricalsignal; an opto-isolator in communication with the MEMS device driverand configured to produce the electrical signal from an optical signalproduced by a light source in response to a current-based controlsignal, such that the light source produces a light beam which istransmitted to a photodetector; wherein the MEMS device driver isconnected to the photodetector and in communication with the MEMS switchto produce high voltage switching logic from the electrical signal. 2.The system of claim 1, wherein the MEMS device driver is positioned inproximity to the photodetector, which results in a reduced probabilityof electromagnetic interference (EMI) coupling with the connectionbetween the MEMS device driver and the photodetector.
 3. The system ofclaim 1, wherein the MEMS switch is configured to reversibly create adisconnect in the resonant loop to vary the receiving coil between thefirst state and the second state.
 4. The system of claim 1, wherein thecurrent-based control signal provided to opto-isolator has a current ofbetween about 5 milliamps (ma) and 20 ma.
 5. The system of claim 1,wherein the MEMS device driver and the opto-isolator are disposedbetween about 1 mm and 20 mm from each other.
 6. The system of claim 1,wherein the opto-isolator comprises the light source and thephotodetector, and the photodetector is in communication with the devicedriver, the photodetector being operable to produce the electricalsignal at between about 1 nanoamp (nA) and 5 nA of current at a voltageof between about 50 volts (V) and 150 V.
 7. The system of claim 1,wherein opto-isolator, the MEMS device driver, and the MEMS switch areintegrated into an electrical package that is configured to interfacewith the receiving coil.
 8. The system of claim 1, wherein the MEMSdevice driver comprises metal oxide semiconductor field effecttransistor (MOSFET) totem pole drivers configured to produce the logicsignal.
 9. The system of claim 8, comprising control circuitryconfigured to send the current-based control signal to the opto-isolatorto cause the MEMS switch to vary the receiving coil from the first stateto the second state when the transmitting coil is transmitting RFenergy, and to vary the receiving coil from the second state to thefirst state when the transmitting coil is not transmitting RF energy.